[RTW] Review of draft-holmberg-rtcweb-ucreqs-00 (Web Real-Time Communication Use-cases and Requirements)

[Harald Alvestrand]

On 03/15/11 07:27, Christer Holmberg wrote:
> Hi Harald,
>
>>>>> Even if only talking about codecs, we also need to talk how deep into detail we want to go.
>>>>>
>>>>> For example, things like: "codec X can only be used when codec Y is not used" etc.
>>>> Is there a real life example of this situation, or are you just imagining the possibility?
>>> H.245. Probably you can do it with SDP CapNeg also...
>> Not whether you can express it - is there a real life situation on a real life device where you are capable of using two codecs, but not at the same time?
> I think the following are valid real life situations:
>
> - Device restrictions (CPU, DSP etc)
> - Network restrictions (bandwidth etc)
> - Number of streams
I think it's possible to construct devices for which this can be a 
problem, yes.
That's not what I was asking.
To be even more specific:

Do you know of ONE device, presently existing in the Real World (that 
is, outside of labs) that supports TWO specific, different codecs, and 
is able to use either of them, but is not able to use them at the same time?

If the name needs to be witheld, that's fine, but I would very much like 
to see if this is a requirement that comes out of experience, or if it 
is a problem we just imagine could happen.

Network, bandwidth, processing power and so on restrictions are usually 
a problem even if the same codec is used for all streams, so that is 
something we have to deal with. I'm specifically trying to figure out if 
we have a requirement driven by a real life scenario for "you can choose 
this codec, or you can choose that codec, but you can't choose both".

My reason for drilling down so hard on this is that a requirement to 
express set difference complicates a negotiation language by a rather 
large amount compared to just doing set intersection.
(The problem is most acute when dealing with ACLs, where adding set 
difference usually makes it impossible for an administrator to figure 
out what exactly he's specified for any rule set of some complexity, but 
it's a problem for any such language.)

                    Harald